Method for making granular superphosphate



Jan. 21, 1947. M. sHor-:LD

METHOD FOR MAKING GRANULAR SUPERPHOSPHATE Original Filed June 15, 1938 Patented Jan. 21, 1947 .METHOD FOR MAKING GRANULAR SUPERPHOSPHATE Mark shoela, Baltimore, Ma., assignor to The Davison Chemical Corporation, Baltimore, Md.

Original application JuneI` 15, 1938, Serial No. 213,925. Divided and this application March 23, 1939, Serial No. 263,756

This invention relates to the manufacture o granular superphosphate.

This application is a true division of my application Serial No. 213,925; filed June 15, 1938.

In the manufacture of granular superphosphate, a preferred form of process is one in which the superphosphate, with sufficient water, is agitated to produce agglomerated particles. These agglomerated particles are then subjected to a drying step under further agitation to form h ard, dry granules. Ordinarily, this type of process is carried out in apparatus which comprises a rotary drum in which the particles are agglomerated. Particles thus agglomerated are subjected to the drying step in another rotary heated drum.

Another form of process comprises agglomerating or conditioning and then drying in the same rotary drum in different sections of the drum. An aqueous medium may be added to produce the desired initial moisture content to assist in the agglomeration.

The granular `superphosphate obtained comprises hard, dry, globoid, nodular, encrusted and indurated particles having several times the crushing strength of ordinary fully cured den superphosphate.

When fresh superphosphate directly from the den is charged into the conditioner of the granulating unit, there is in many instances sufficient variation as to physical condition of the den super to make this operation impractical. The difllculty is that at times the agglomeration in the conditioner is excessive so that large lumps form, and occasionally a clayey mass is formed. This causes trouble due to sticking of the material in the conditioner and the dryer, and the nal material is too large and non-uniform as to size and moisture content. When the material from the dryer is too large the amount of dust produced during the subsequent milling operation is excessive. Up tothe time of this invention it was necessary to putthe fresh super into preliminary storage or to rasp and aerate it, so as to allow proper control of particle size in the conditioner. This procedure entailed, of course, considerable extra cost due to the rehandling of the material and storage facilities required.

By means of this invention, fresh den super can be transferred directly from the den to the conditioner, and the particle size from the conditioner can be controlled within the accuracy that the commercial application of the process 8 Claims. (Cl. 71-40) requires. I'his is accomplished by feeding in a determined amount of dry material to the feed end of the conditioner where it enters with the fresh den super.

The maximum capacity of the granulating `unit is obtained by using super from a stationary den, unshaved and unrasped, because lthe den super is at the maximum possible temperature. `It is therefore important, if maximum capacity is desired. to avoid storing or rasping the super prior to granulation. Using this invention it is possible to do so. In other words there is not only saving due to elimination of handling, rasping and storing charges, but the capacity of the granulating unit is also increased.

Any dry, or reasonably dry, material may be used as the additive, as for instance sand, if it is required to cut the concentration of P205 in the final product. Well cured den super may be used. The most suitable material is,l however,

classifier dust, which is obtained in the following manner: l

The 4granulated material from the unit goes to storage for a minimum of approximately 10 days. When shipping granular superphosphate, the material from storage is passed over a screen to eliminate any oversize. This oversize goes to a mill, is crushed, and is returned to the screen. The entire product from the screenis passed through a pneumatic classifying system where substantially all fines are removed. 'I'he dust free material is discharged into bags ready for shipment. The amount ofclassier dust may vary from 10 to 20% of the total production.

Instead of using pneumatic classification, double screening may be used. The net result will however be approximately the same.

The classifier dust may be sold by itself or mixed with regular den super and sold as run of pile or cut to 16%. vThe advantage of using it back in the granulating system is however quit considerable as has been pointed out above. Moreover, the dust has a high percentage of available P205.

' As an addition substance, dry phosphate rock may be used and this material is particularly suitable when it is desired to make cut superphosphate in territories whereit is undesirable to add sand a-s filler. An additional advantage is obtained when the ground phosphate rock is used because some of the P205 in this becomes available without the use of any extra sulphuric acid. In other words when phosphate rock has to be used to produce a cut grade of granular superphosphate there is a. distinct acid economy obtained. i

Among the objects of the invention are to reduce handling. save time and cost of production. and insure a more uniform product.

Other objects will be apparent from the description of the apparatus used and the process as set forth.

The single ligure of the drawing is a diagrammatic illustration of a form of apparatus which I may employ, the apparatus being shown in section.

Referring to the drawing, I have shown a conditioner I and a drier 2. The conditioner I comprises a hollow metallic cylinder 3 having rings 4 thereon which are adapted to roll on rollers .5 mounted on supports 5'. There are a plurality of rollers at each ring 4. The metallic cylinder 3 is rotated by means of a ring gear 6 driven by a pinion 6' mounted on the shaft of a motor 1. It is to be understood that reduction gearing may be employed between the motor and the pinion 6', but for purposes of illustration no such reduction gearing is shown. The metallic cylinder is provided With a partially closed end 8 having an aperture 9 therein into which sticks a spout I0 of a hopper I I. A slat conveyor or belt I2, which is adapted to be driven from some source of power, not shown, conveys fresh den superphosphate I3 from a, superphosphate hopper I4. The superphosphate is delivered to the hopper I4 by means of a clam shelly bucket which takes the material directly from the den, or some other means of transportation may -be employed.

There is a sliding door I5 provided in one side of the hopper I4 adjacent an aperture I6. The door I5 is provided with a handle I1. By raising or lowering the door I5, the amount of fresh den superphosphate I3 which is conveyed by the slat conveyor I2 can be determined.

Fed also into the hopper I I is a dry, finely divided material I8 whch may be sand, fully cured superphosphate, classifier dust, ground phosphate rock, or some other similar material. This material I8 is fed by means of a screw conveyor I9 operating in a conveyor box 20 located at the bottom of a hopper 2|. The screw I9 is rotated by means of a gear 22 meshing with a pinion 23 driven :by a variable speed motor 24.

Adapted to discharge an aqueous medium into the conditioner I are pipes 25 having nozzles 26. Valves 21, which may be manually operated by an operator control the amount of aqueous medium discharged into the interior of the conditioner I.

Mounted on an instrument panel 28 are meters 29 and 30. The meter 29 is connected electrically to a pyrometer 3l located in a. refractory lined combustion furnace 32, heated by a gas burner 33. The meter 30 is electrically connected to a thermometer 34 which is located in a discharge breeching 35 which covers the end of a rotary cylinder 36 which forms the drier 2. The temperature of the hot gases entering the drier 2 and leaving the drier 2 are readable on the meter faces 29 and 30 respectively.

Mounted on the instrument panel. 28 is a flood light 31 which is directed into the open end of the conditioner I. A supporting platform 38 is located adjacent the open end of the conditioner I. The conditioner I is slanted downward from the end into which the fresh den superphosphate is discharged. An operator standing on the platform 38 at all times can visually inspect, by means of the oodlight 31, the interior of the conditioner I, and regulate by means of valves 21 the condition of the material in the conditioner I. The operator must be present on the platform at all times and by adjustment of the regulating valvesv 21, he maintains a constant physical condition of the material leaving the conditioner and entering the drier.

In the operating floor is a trap door 40 which is on hinges and provides easy access to a cleanout door v4I in a water-jacketed chute 42. A wall 43 forming the vertical upper section of chute 42 prevents the conditioned agglomerated particles from falling out of the upper end of thev chute.

The water-jacketed chute 42 is provided with a water jacket 44 in which cooling fluid is circulated to prevent overheating of the chute. The connections for sending the fluid through the water jacket are 4not shown. The lower end of the chute discharges into the upper end of the drier 2, which has an aperture 45 into which the lower end of the chute projects.

'I'he rotary cylinder 36 which comprises the drier is slanted from the horizontal and is provided with rings 46 adapted to be supported by rollers 41 mounted on supports 48. As is the case with the construction of the conditioner I, there are a plurality of rollers 41 at each station to 'rotatably support the rotary cylinder 36. To rotate the cylinder 36 of the drier 2 I have shown a ring gear 49 driven by. a. pinion 50 mounted on the shaft of a motor 5I. Here again reduction gearing may be used if desired, but such a construction is not shown in order to simplify the illustration of the apparatus.

The discharge breeching 35 is connected to'A a pipe 52 which leads to the suction side of a blower 53 which is adapted to suck the gases through the pipe 52 and discharge them through a pipe 54. The blower 53 is mounted on a platform 55 upon which are mounted the supports 5 for the.

rollers 5 in which the conditioner unit is adapted to be rotatably supported.

The discharge breaching 35 is provided with a discharge chute 56. Mounted on the discharge chute 56 is a swinging door 51 which prevents the blower 53 from sucking too much fresh air into the discharge breeching 35. By this construction of the swinging door a suction is created in the interior of the drier 2 and the gases from the interior of the drier 2 are discharged through the pipe 54. The dried granular particles are delivered into a receiving pit 58 from which they may |be taken by means of a clam shell bucket, or some other conveying mechanism.

Fresh unrasped super I3 direct from the den is charged into hopper I4. The den super may as an example have the following average composition:

i Y Per cent Moisture 10.56 Total P205 20.03 InsoLPzOa 3.04 AvaiLPzOs 16.99

for instance may analyze as follows:

Per cent Moisture 1.7 Total P20#- 21.3 InSOl. P205 1.2 Avail. P205 20.1

Conveyor feeder I2 and screw feeder Ilare so adjusted that the classifier dust represents 10% of the total feed. In other words. the ratio of fresh super to classifier dust is 9 to 1 by weight.

The amount of water added tothe material in' the conditioner through sprays I averages approximately 1.2%. This does not mean that there is a uniform addition, because the operator on the platform gives constant attention to the physical condition of the material in the conditioner and regulates the amount of water by means of valves 21, so that every minute of the day visual observation governs the proper physical condition of the material going to the drier. The instant Water additions may vary from practically nothing to 2% or more. The range is generally from about A to 2%.

This water addition is so critical for proper operating conditions that a small fraction of a percent will produce a major change of physical condition of the material,

'Ihe average addition of about 1.2% mentioned above, with the given average composition of the above given example. Set forth in a sonicsuper and classifier dust, meansthat the mate-- rial from the conditioner to the drier has an average moisture content practically identical with that of the super fed or 10% This clearly brings out the point that the classier dust addition is for the purpose of regulation, which is of paramount practical importance for the successful commercial carrying out of the process.

The granulated super from the drier has the l following composition:

Per cent Moisture 5.15 Total Pz0= 21.08 Insol. P205 2.75 Avail. P205 18.33

This material is allowed to stand in storage for a minimum of approximately 10 days. After passing through the shipping unit the final material in the bags analyzes as follows:

Per cent Moisture 1.67` Total PzOf. 21.44 Insol. P205 1.18 Avail. P205.. 20.26

It will lbe noted that the acidulation is regulated so that the final product is just above 20% available P205. 'I'he reason for this is that 20% is the standard commercial gradethat has been l established for granular superphosphate,

In connection with the moisture changes in the material during the process, the following is of interest:

The fresh den super has a moisture content of about 101/2 The material from the conditioner to the drier has the same average moisture content or 101/.'2%. The granulated super from the unit shows about 5% moisture. The moisture elimination in the drier is therefore about 51/2`%. The shipping material has a moisture of about 11/2%. There is therefore an apparent difference of Ill/2% moisture between the material from the granulating unit and the material as shipped. Careful investigation has shown that thetrue moisture loss between these two points is only 11/% and is due to handling and ture to that what simpler manner of acidulation during the various steps of the process the result is as follows:

Percent acidulation available P205 as a percentage of the total P20. 'I'his may be written:

% available P30; total P305 By the accurate-control of the moisture content and the general consistency of the fresh den superphosphate at the agglomerating step, a substantially uniform agglomerated material is delivered from the conditioning step to the dry` ing step. A final granulated product is obtained in which there is a minimum of variation in particle size with a relatively small percentage of fines or oversized particles.

While I have shown a process and apparatus which are illustrative of my invention, it is to be understood that I am to be limited only by the scope of the appended claims and the showing of the prior art.

I claim:

1. A method of manufacturing granular superphosphate comprising adding classifier dust to fresh superphosphate, then adding an aqueous medium to bring the mixture to the moisture content of the fresh superphosphate, agglomerating the mixture. and then drying the agglomerated particles.

2.- A method of manufacturing granular superphosphate comprising adding approximately 10% by weight of classifier dust to fresh 'superphosphate, then adding an aqueous medium to bring the mixture to the moisture content of the fresh 3. In the manufacture of granular superphosphate,controlling the consistency of superphosphate fresh from the den to enable the agglomeration of particles of substantially uniform size by mixing classifier dust with the fresh superphosphate, aqueous medium to bring the moisture content of the mixture to 'about the same as that of the fresh superphosphate, then agglomerating by agitating, and then drying while agitating.

4. In the manufacture of granular superphosphate, controlling the consistency of superphosphate fresh from the den to enable the agglomeration of particles of substantially uniform size' by mixing classiiler dust with the 4fresh superphosphate, then adding an aqueous medium to bring the moisture content of the mixof the fresh superphosphate, agglomerating the material by tumbling in a rotary drum, and drying the agglomerated particles while tumbling in a rotary drum.

5. In the manufacture of granular superphosphate, controlling the consistency of superphosphate fresh from the den to enable the agglomeration of particles of substantially uniform size by mixing 10% with the fresh superphosphate, then adding an aqueous medium to bring the moisture content of the mixture to that of the fresh superphosphate, agglomerating the material by tumbling in aroon the basis of Percentage then adding about 2% of an A by weight of classifier dust 6. A process for producing granular super-v phosphate from superphosphate fresh from the den comprising feeding the fresh superphosphate to a rotating drum that is slanted to the horizontal, together with classifier dust, introducing into the drum a quantity of an aqueous medium to bring the moisture content of the mixture to that of the fresh superphosphate, passingvthe agglomerated particles from the conditioning step in this drum to a second drum where the particles are subjected to a drying step and elevated temperatures to form hard, dry, encrusted and indurated globule particles of several times the crushing strength of fully cured den superphosphate.

7. In the manufacture of granular superphosphate, controlling the consistency of supersize by mixing 10% by weight of classier dust with the fresh superphosphate, then adding an aqueous medium. then agglomerating by agitating, and then drying while agitating.

8. A process of treating den superphosplate to produce a ygranular superphosphate fertilizer in hard, dry, globoid. nodular, encrusted and indurated particles having several times .the crushing strength of ordinary den superphosphate comprising adding 10% by weight of classifier dust to the den superphosphate, adding approximately 2% oi. an aqueous medium to the mixture thereby raising the moisture content of the mixture to around 10i/2%. forming the mixture into agglomerated particles, tumbling the agglomerated particles in a zone of hot gases until the moisture content of the agglomerated particles is reduced to approximately 5%, and discharging the particles from the drying zone. v

MARK SHOELD. 

